Trundles Cylinder Head Coolant Bypass for Nissan Patrol TD42 Genuine HeadCylinder Head Coolant Bypass to suit Nissan TD42 Engines Includes: 1x Cylinder Head Coolant Bypass for Genuine TD42 Head Details Designed to help reduce the micro boiling points in the TD42 Pre Combustion chamber areas in head The genuine head fitting suits OEM heads with 34. 9mm frost plug The aftermarket head fitting suits heads with 36mm frost plug Note: You will need to tap a M6 hole in the back of your head and a 1 4" NPT in your thermostat